Study Of Transition Resistance Calculation Method Based On Two Terminals’Time-domain Signals

Short-circuit faults of power system are generally non-metallic, and there is transition resistance at the fault point. When short-circuit fault occurs, the short-circuit current will flows from phase to ground or from one phase to another phase, the resistance of the path is called transition resistance, which includes arc resistance, intermediate material resistance, resistance between conductor and ground, metal tower grounding resistance and so on. At present, all of the research and analysis of the domestic and foreign treat transition resistance as pure resistance. Transition resistance has bad effect on power system fault analysis, protection setting calculation, and the correct operation of the protection devices. Many misoperations and refusals to operate of protection devices relate to transition resistance.Transition resistance has strong randomness and unpredictability, especially when arc short circuit fault occurs, transition resistance will be intermittent and change significantly. Online and real-time calculation of transition resistance can help operating personnel to analyze power system accurately, grasp the characteristics of transition resistance and has great importance to improve the reliability of the operation of protection devices.In order to calculate transition resistance quickly and accurately during short circuit fault, a calculation method based on two terminals’time-domain signals is proposed. If fault type is known, the new method uses π type equivalent model and time-domain signals during the fault to calculate transition resistance online by solving differential equation of the circuit. The single-phase system is taken as the example to show the calculation process, then by using phase-model transformation method and composite modal network, we can get the transition resistance calculation method of three-phase system. This calculation method has the characteristics of short response time and high calculation accuracy, it is independent of fault location, non-periodic components and harmonics. PSCAD/EMTDC simulation software is applied to study some cases, and the simulation results verify the effectiveness and accuracy of the proposed method.In order to calculate transition resistance quickly and accurately after the circuit breaker trips when single-phase short circuit occurs, a calculation method based on two terminals’time-domain signals is proposed. The new method uses π type equivalent model, takes the branch which contains transition resistance as the research object and calculate transition resistance by solving differential equation of the circuit. The new method requires the result of fault location, existing fault location technology can meet the accuracy requirements of the method. The new method has the characteristics of short response time and high calculation accuracy, it is independent of non-periodic components and harmonics. PSCAD/EMTDC simulation software is applied to study some cases, and the simulation results verify the effectiveness and accuracy of the proposed method.In order to get the result of fault location quickly and accurately when single-phase short circuit occurs in distribution network, a new method is proposed. The new method uses distributed parameter model and ignores the coupling effect, derives the computation expression of transition resistance. In the premise of transition resistance being pure resistance, fault distance is calculated by iterative method. PSCAD/EMTDC simulation software is applied to verify the effectiveness and accuracy of the proposed method. A new fault line selection criterion based on the simulation results is proposed. Large number of simulation is applied to verify its correctness.